This invention relates to a method for enhancing the lightfastness of dyed nylon textile fibers.
Heretofore, it has been known to improve the lightfastness of dyed nylon fabrics by treating the fibers with aqueous solutions containing copper in the form of cupric ion. The copper was applied as a water soluble copper salt, usually copper sulfate or copper acetate that was added directly to the dyebath and deposited on the fiber simultaneously with the dye. But because the copper is soluble, it has a very poor affinity for the nylon, and therefore any absorbed copper can be easily washed off the fiber in the normal wet treatments to which fibers are subjected in processing. This results in uneven distribution of the copper on the fiber and its impact on lightfastness will not be uniform.
In addition, because of its high solubility, the use of the soluble copper salts gives rise to effluent problems in disposing of spent dyebath liquors and the water used in washing the dyed fabric. Moreover, when soluble copper salts are added to the dye baths, in many commonly used dyeing processes, the pH conditions during the dyeing cycle are such that the copper can precipitate as copper hydroxide, which, in temperatures are employed to accelerate the exhaustion and fixation of the dyes on the fiber. Copper oxide objectionably discolors the dyed nylon (imparting a black or brown coloration thereto), does not exhaust in a level manner, and frequently "builds up" on and contaminates the dyeing vessel.
To solve the above problems, U.S. Pat. No. 4,253,843 teaches the use of copper phosphate, which is now being successfully employed by the industry. However, several important problems remain to be overcome. One is the need to adjust the pH very carefully to form colloidal copper phosphate which then exhausts onto the nylon substrate. This is not always easy under prevailing industrial conditions. Moreover, the processing conditions may require pH values at which copper phosphate becomes soluble and is partially extracted from the fiber into the treating bath. This in itself is not an important problem from the standpoint of lightfastness enhancement because an excess of copper phosphate may be used; however, it creates an environmental problem when the bath is disposed of since copper is a regulated water pollutant.
To obviate the copper pollution problem in manufacturing facilities that have no means to control such pollution, it was attempted to spray acid solutions of copper phosphate, and other soluble salts such as copper sulfate, onto the dyed nylon substrate before the drying step. Such a method would deposit all the copper onto the nylon substrate without losses into the environment.
Unfortunately when spraying and drying such copper salt solutions, especially strongly acid solutions, we encountered objectionable discoloration of the dyeings, harshness of hand and, occasionally insufficient lightfastness improvement.
In attempting to solve some of the above problems, a number of inventions have been granted patents in recent years, such as U.S. Pat. Nos. 4,383,835; 4,544,372; 4,613,334. The commonality of all these patents is the use of water-insoluble copper complexes which are applied in the form of solid dispersions in water. These products generally require no accurate pH adjustment and are insoluble in a wide pH range. However, none of these products exhausts on the nylon substrate completely (to a 100% exhaustion) and thus copper is still found in the effluent after their application. Moreover, these solid dispersions in water are insufficiently stable to afford the possibility of spray application because they will build up in the spray nozzles and eventually obstruct them. They could be applied by padding, but dipping and squeezing a textile substrate always results in residual liquid which must be discarded. The residual liquid cannot be reused in most cases because it becomes contaminated with dye from the treated substrate. Also, pad applications will deposit too much moisture which must then be evaporated, resulting in extra time and energy costs.